Method and means for repelling animals

ABSTRACT

For repelling elk, hart, roe deer and similar animals from plantations, orchards, road sections etc. one or more natural or synthetic steroids of the type occurring on human skin or hair or in human sweat or urine are used. Also derivatives of these steroids obtainable by subjecting the steroids to air, moisture or micro-organisms may be used. The steroids are combined with a carrier into a repellent unit which may liberate molecules of the repellent substance to the air for maintaining a concentration perceptible to the sense of smell of the animals.

In modern society conflicts may easily arise between different interestswith respect to the use of natural resources such as forests, meadowsand fields. The parties in this conflict may be numerous, and theindividual citizen will often belong to different sides according to theactivity exercised at the moment. A rich animal life is for instancevery gratifying for those interested in hunting, but constitutes aproblem to road users and may cause browsing damages in fields, forestplantations and gardens.

The growth in the number of elk and roe deer has accelerated in thelater years, partly because of various game encouraging measures. At thesame time the frequency of accidents caused by collision between theseanimals and cars has become greater and grown into a serious trafficproblem (The Highways Department of the Swedish State: The Game AccidentProject, May 1980). Even half-wild animals, such as reindeer in thenorthern part of Scandinavia, cause similar difficulties for thetraffic.

Admittedly, browsing damages by elk, roe deer and other wild animals onforest plantations, fields and gardens do not involve personal injuriesor death, but has because of the increase in the stock of animals grownto such a size that they are significant both from a private and asocial economic viewpoint. It is therefore natural that great effortsare made to find methods for keeping wild and half-wild animals awayfrom the areas which they damage.

The largest effort, at least from a quantitative viewpoint, has beenmade in connection with game and highway traffic. Acoustic, optical andchemical methods have been used in addition to fences along certainhighways. The optical repellent means, primarily game mirrors, havelargely proven to be without effect since after a short familiarizationperiod the animals do not mind the mirrors any longer. Also for theacoustic methods tested the familiarization is so fast that the methodsare completely without effect in practice.

If fences are made sufficiently high and close, they are effective atleast as far as larger animals such as elk and roe deer are concerned.However, cost reasons and the fact that fences hamper outdoor life,indicate that this method for avoiding game accidents cannot be used butto a very limited extent (The Highways Department of the Swedish State:The Game Accident Project, May 1980).

Experiments with smelling repellent means against wild animals have beenconducted by numerous parties. Special reference is made to anexperiment in which cresol, isobutylalcohol, hartshorn oil, blood meal,thiram and butyric acid have been used as a repellent means against elk.In some cases a certain repellent effect has been observed. However, theexperimental design has been such that no definite conclusions aboutfamiliarization and other long term effects have been possible (HansRosengarten, University of Stockholm, Experiments with SmellingRepellents against Elk, January 1979).

It is known that animals often react to the smell of beasts of preyusually attacking the animal species by running away. Any hunter andoutdoor person is familiar with the fact that most wild animals avoidcontact with human beings, and that it is the smell which to a greatextent makes the animal aware of the presence of human beings. In almostevery case, approaching a browsing roe deer in following wind results ina flight reaction, whereas a corresponding attempt in headwind has apossibility of succeeding if normal care is observed. The tendency ofthe animals to run away when noticing human smell has been utilized bysuspending human hair in order to keep fissiped game away from orchards(Cultivation of Fruit and Berries, No. 5, 1979/No. 1, 1980).

It should be observed that the ability of the animals to perceive smellsis usually substantially greater than that of human beings. When smelland smell substances are referred to in the preceding and the subsequentparagraphs, the perception of the animals is referred to. The substancesreferred to as smell substances may sometimes be taken as completelyodourless to the less developed sense of smell of human beings. There isreason to believe that the flight reaction of the animals in response tosmell of human beings and beasts of prey is instinctive and inheritedand to a great extent independent of previous contact with beasts ofprey or human beings. If a similar reaction could be used for repellentpurposes, advantages such as a reduced risk of familiarization areobtained.

The exact chemical composition of human smell is largely unknown.However, it may be presumed that there are large variations betweenindividuals, and that there are also systematic differences due to age,sex and race. It is known that a large number of various substances maybe found in the various secretions from the human body, for instance insweat and urine. Some of these substances are perceived as odourous bycertain persons, whereas others classify them as odourless. However,there are good reasons to believe that there exists a basic structure ofsmells which characterizes the human being as a species. The compoundsin this smell originate from various secretions, primarily from sweatand urine. With respect to sweat the secretions from the so calledapocrine sweat glands are of special interest. In human beings thesesweat glands are present primarily in the arm pits and in the areaaround the anal orifice and the genitals. Apart from the directsecretions from the human body also such decomposition products whichmay formed from these secretions under influence of air, humidity andmicro-organisms, especially organisms included in the normal skin flora,probably form part of the smell specific to the species.

Many of the components found in human sweat and urine have also beendemonstrated in other mammals. At least some of the substances which maybe expected to form part of the smell specific for the specieschemically belong to the group of steroids, and many of them havehormonal character. Even the amount of secretion from the apocrine sweatglands is small, and the content of steroids in these secretionsconstitutes a small fraction of the total amount in the order of 0.02%.This amount is in turn composed of several different steroids, and itmay therefore be expected that the amount of individual steroids insecretions from the apocrine sweat glands in human beings is in theorder of some picograms or in some cases possibly around one nanogram.Also in the urine the amounts are small, at least if some specificpregnancy hormones in pregnant women are excepted. The occurrence ofsteroids in secretions from the apocrine sweat glands, which mustprobably be regarded as the "smell glands" of humans similar to thecorresponding glands in other mammals, makes it probable that steroidsconstitute a not insignificant part of the smell specific for thespecies. Differences between various mammals with respect to the smellshould then be referred to the amount and balance between the variouscomponents.

In human sweat and urine the following steroids have been determined:

androst-4-en-3,17-dione,

androsterone,

dehydroepiandrosterone,

preg-5-en-3β-ol-20-one,

5α-androst-16-en-3α-ol,

5α-androst-16-en-3-one,

testosterone,

11-keto-aetiocholanalone (3α-hydroxy-5β-androstan-11,17-dione),

i-androstanalone,

oestrone,

oestriol,

oestradiol,

androstan-3-one,

16-androstene-3-ol,

progesterone and

pregnandiol.

As oxidation products

androstadien-17-one and

androst-2-en-17-one

have been reported.

With a view to the complicated composition of the secretions from humansmell glands, i.e. the apocrine sweat glands, it is surprising thatindividual components and combinations of a few components of thesecretions have proved to exhibit repellent effects on animalscomparable to or exceeding the effect of human smell from for instancesuspended used working cloths and human hair. The substances, therepellent effect of which in this respect has been studied in detail,all chemically belong to the group of steroids and are synthetic orsemi-synthetic substances corresponding to the steroids which have beendemonstrated in human skin and hair, including body hair, or in humansweat or urine.

Means containing steroids which may be of a hormonal character have beenwidely used both in medicine and in domestic animal care.

Individual steroids and compositions containing two or more steroids arecertainly well applicable to obtain a repellent effect on wild animals.However, the sometimes high biological activity of the steroidsconstitutes a handling problem. The high costs of producing steroidsalso indicate that an attempt must be made to obtain an optimalutilization by controlling the liberation to the atmosphere in asuitable manner. The problems involved in the handling of the steroidsand in the control of the liberation to the atmosphere are best solvedby combining the steroids or the steroid composition with a carrier intoa repellent unit.

The choice of carrier and the design of the repellent unit may beeffected in many different ways which are adapted to various conditionsof use. However, an essential condition is that the repellent unit, i.e.the combination of the steroid preparation and the carrier, can liberatesteroid molecules to the air at a controlled rate so that a sufficientlyhigh and uniform concentration can be maintained in the air surroundingthe repellent unit in a desired period.

The present invention relates to a method for repelling animals,characterized by the use as a repellent substance of one or moresteroids which are synthetic or have been extracted from naturallyoccurring materials, and which are of the type occurring on human skinor hair or in human sweat or urine and/or one or more of the derivativesthereof obtainable by subjecting the steroids to air, moisture ormicro-organisms, in such a manner as to provide in the air aconcentration perceptible to the sense of smell of the animals.

The invention also provides a means of repelling animals, characterizedin that as a repellent substance it contains one or more steroids whichare synthetic or have been extracted from naturally occurring materials,and which are of the type occurring on human skin or hair or in humansweat or urine and/or one or more of the derivatives thereof obtainableby subjecting the steroids to air, moisture or micro-organisms, and thatthis repellent substance is combined with a carrier into a repellentunit capable of liberating molecules of the repellent substance into theair for maintaining a concentration perceptible to the sense of smell ofthe animals.

It is possible to extract the said steroids and their derivatives fromhuman sweat and urine, but for obvious reasons only synthetic productsare used in practice. Raw materials for the synthesis may for instancebe steroid-alkaloids which may be recovered from certain plant parts orcholesterol. Also fully synthetic methods using petroleum products asstarting materials are possible. The methods of the synthesis may bepurely chemical, biochemical or microbiological or various combinationsof these methods. In some cases it may be advantageous to use anintermediate product from the synthesis, deleting for instance the finalseparation or purification step.

As indicated the naturally occurring amounts of steroids in humansecretions are very small. Considering that relatively large moleculesare involved, their vapour pressure must be presumed to be very low.However, it is known that the sense of smell of animals and human beingsis often so sensitive that no measuring instrument comes up to it. Theexperiments carried out have not made it possible to establish any lowerlimit for the amount below which no effect of the said steroids may beobserved. However, it can be assumed that any such limit lies below thelevel corresponding to the presence of the steroids in human secretions.For reasons of handling and because of the wish to maintain asufficiently high concentration in the atmosphere in a not too shortperiod, the amounts used cannot be too small. A practical lower limitshould be about 1 ng of steroid for each repellent unit.

It is in the nature of the case that the amount used for each repellentunit should be kept as small as possible, not at least for cost reasons.However, as far as it has been possible to ascertain there are nothingindicating that large amounts should have negative effects from atechnical point of view. It is therefore not possible to state any upperlimit since it would be completely dependent upon how the means is to beapplied and how long it is desired to maintain the repellent effect. Inpreferred embodiments of the invention the steroid amounts have variedbetween 0.1 μg and 100 mg, preferably between 1 μg and 100 mg for eachrepellent unit.

The steroids occurring on human skin and hair and in human sweat andurine can at least in part have hormonal properties. When carrying outthe present invention a hormonal effect is an undesired side effect. Forthis reason it is preferred to use steroids having as small a hormonaleffect as possible.

In practical experiments various steroids including the following havebeen used: testosterone, androsterone, dehydroepiandrosterone,11-ketoaetiocholanalone, i-androstanalone, oestrone and androstenol.These steroids are the quantitatively most significant in secretionsfrom apocrine sweat glands in male human beings.

Dehydroepiandrosterone and androsterone combine a relatively lowhormonal effect with a very good repellent effect. They mayadvantageously be used either separately or in combination with eachother and/or with other steroids. Combinations of two or more steroidsare often preferable, since they supplement the repellent effect of eachother and provide a repellent smell which is closer to the smell ofhuman beings. In this manner a synergetic effect may be obtained whichabove all is reflected in a reduced tendency of familiarization. Thecontent of the individual steroids may also be kept lower, which reducesthe risk of specific hormonal effects in the production and handling.

As already mentioned it is advantageous to combine the said steroidswith a suitable carrier when carrying out the invention in practice. Onepurpose of the carrier is to protect the steroid preparation againstloss by mechanical contact. The carrier should further protect thesteroids against moisture which may release active substance and lead toinactivation of the repellent effect. However, the most important effectof the carrier is, together with the steroid preparation, to form acombination which liberates steroid molecules to the air at a rate whichis controllable to as large an extent as possible.

The combination of carrier and steroid composition is in practical usesubjected to very different conditions with respect to temperature, airflow etc. An increase of the temperature raises the vapour pressure ofthe steroids, whereas an increase of the air velocity enhances theliberation of active material by reducing the degree of saturation overthe preparation. Both effects result in faster consumption of therepellent substance. Whereas an increased liberation of steroidmolecules to the atmosphere may be desirable and necessary at increasingwind velocity in order to compensate for the dilution caused by thehigher wind velocity, the increase at higher temperatures is presumablynot desirable. It may be convenient to modify the vapour pressure of thesteroid composition, for instance by dilution with some form of solventwhich may be present in solid or liquid form. By a suitable choice ofdiluent it is also possible to see to it that the liberation at lowtemperatures is not reduced to unacceptably low values.

Other possibilities of control with the rate of liberation involvescontrolling the liberation to a larger or lesser extent by diffusion,for instance by making the carrier of a microporous material or byencasing the steroid preparation in a membrane having a limitedpermeability. Other embodiments in which the diffusion may provide asubstantial part of the control mechanism for liberation of repellentsubstance involve letting the steroid composition and the carrierforming a gel which may be shrinking or not shrinking depending onwhether or not also other components are liberated to the atmospheretogether with the steroid molecules.

A further possibility for controlling the liberation rate is to usecarrier materials having the capacity of absorbing the repellentsubstance and having a large surface area for each unit of volume, forinstance activated charcoal or colloidal or pyrogenic silica. A largenumber of different methods for controlling the liberation of activesubstances to the environment are known, and it does not causesubstantial difficulties for a man skilled in the art to combine variousmethods in a convenient manner in order to achieve the desired result.

With respect to the choice of material for the carrier there are inprinciple no restrictions. As an example porous ceramic bodies, nativeor regenerated cellulose, natural or synthetic polymers of various typesin filament form or as microporous or macroporous moulds or as gelforming substances may be used. There may further be used inorganicmaterials having a large specific area, for instance certain silicacompounds such as zeolites, fine-grained clays etc. In many cases it isadvantageous to use several different materials in combination to obtainthe desired result. The technique in this respect is well known to thoseskilled in the art.

Whereas the steroid preparation and the carrier should be combined inprotected environments, for instance in a laboratory or in amanufacturing plant, the final shaping may take place either in directconnection with the combination of the steroid preparation and thecarrier or locally when applying it to the final place of application.

In the former case a moulded body is produced which may have any desiredshape, for instance tape, strip, sheet, plate, rod, tapering orspherical form. This moulded body is advantageously provided with somecasing protecting against precipitation and preventing direct contactwith the steroid containing body, while still allowing passage ofsteroid molecules in vapour form. Further, the casing should be providedwith some form of suspension or fastening device or be designed so as initself to provide a fastening device in order to permit a stablepositioning in the place of application. Suitable embodiments includetapes or strips which are wound around tree trunks, posts etc. andfastened by adhesion, nailing or tieing.

In the second case the carrier and the steroid preparation are suitablycombined to a viscous liquid or paste, which in the place of applicationis applied directly to solid objects such as posts, tree trunks,mountain shelves etc. The liquid may be applied by being displaced froma container by means of a propulsion gas or by pumping. Anotherpossibility is to effect the application from a tube or a collapsibleplastic bottle. In order to avoid that the persons involved in theapplication are subjected to unnecessary inhalation of the steroids, itis convenient to avoid such spray methods in which the material leavesthe container as an aerosol, whereas pressure containers or pumpsdispensing the material as a foam or a gel string can advantageously beused.

When the material is dispensed in the form of a foam the latter may beof the disintegrating type or of the type forming a permanentmacroporous foam structure. In the local application in a manner asdescribed above, it is often advantageous when the combination of thecarrier and the steroid preparation also contains substances whichprovide a good adherence to the stationary surfaces on which theapplication takes place. Further, the initially liquid or pasty materialshould relatively quickly be transformed into a body which is solid atleast on the surface and which only with substantial difficulty can beremoved from the substrate. By the term "body" in this context alsorelatively thin films such as lacquer coatings are referred to. It is ofcourse possible to apply the combination of the steroid preparation andthe carrier by coating with a brush or a filler knife etc., but this isa less preferred method considering that personnel then has lessopportunity of avoiding direct skin contract with the steroidpreparation.

In the case of local application the term repellent unit may be lessunambiguous. However, it is in the nature of the case that theapplication should take place spot-wise or dot-wise, and the termrepellent unit will then relate to each separate application surface.

If the area to be protected against intrusion by wild animals is verysmall, for instance a small number of fruit trees in a garden in aresidential district, it may be sufficient with only one or a fewrepellent units. In most cases, however, larger areas are involved, suchas forest plantations, large orchards and not at least highwaystrafficked by motor vehicles. In these cases a relatively large numberof repellent units must be placed along the border of the area inquestion. The largest possible distance between the repellent units isthen determined by the strength of the preparations, and a balance mustbe found between the wish to have as few units as possible and theamount of steroids which without hesitation may be placed in a repellentunit. Other factors which also influence the choice of the distancebetween the units and the necessary amount of repellent substance ineach unit are expected normal wind velocities, temperature conditions,requirements for high security against tampering, the required time ofprotection or the period between replacement etc. The distance betweenthe units may in extreme cases be chosen less than 1 m or more than 100m. In ordinary cases the most suitable distance is believed to bebetween 5 and 50 m. Usually 10 to 30 m is a suitable distance betweenthe units. When the substance is applied locally, the shortest of thedistances referred to above is often preferable since it does notsubstantially increase the effort if more units are placed.

At low and medium wind velocities the flow of air is laminar andparallel to the ground. The liberated steroid molecules substantiallyfollow the flow of air and move relatively slowly in vertical direction.For an optimal utilization of the repellent substance it is thereforeconvenient to position the repellent units at a level above the groundwhich is adapted to the animal species to be influenced. A too highpositioning may result in the wind sweeping the steroid molecules awayso that they cannot come into contact with the olfactory organs of theanimals. A too low positioning causes the molecules too soon to comeinto contact with the ground surface where they are bonded andinactivated. For elk and roe deer the most convenient positioning in thevertical direction is between 0.5 and 2.0 m above the ground. It is alsowithin this area that the smell glands of an upright person will befound.

Below a number of examples of the use of steroids and repellent unitsfor keeping roe deer away from gardens and elk and roe deer away fromhighways are given. The choice of the animal species and theexperimental area are determined entirely by experimental considerationsand must not be regarded as limiting, since those skilled in biologywill be perfectly aware of the fact that similar effects may be expectedin other areas and with other groups of animals avoiding contact withhuman beings and using the sense of smell when adapting to thesurroundings. Similarly, it is a matter of course for those skilled inchemistry that other carriers for the steroid preparations will giveanalogical results, provided that the design has been chosen so as tosatisfy the previously mentioned requirements of a continuous liberationof steroid molecules to the atmosphere.

EXAMPLE 1

Extraction sleeves (30×80 mm) were impregnated with androsterone by anaddition of 1 ml of a 1% solution of androsterone.

The repellent units (extraction sleeves) were suspended at intervals of10 m around an orchard, in which browsing damages caused by royal staghad regularly occurred. In an experimental period of 4 days no visits ofroyal stag occurred. The repellent units were then removed and theorchard watched for browsing damages for 4 days. Already the first nightthe orchard was visited by royal stag which caused browsing damages.These visits were repeated for the subsequent days.

Another experiment, this time with extraction sleeves impregnated with10 mg dehydroepiandrosterone, was carried out. Again, no sign of royalstag or browsing damages could be observed during a period of 4 days.During a new control period without the suspended repellent units, thestags returned to the orchard already the first night and causedbrowsing damages. The browsing continued for the subsequent nights.

The experiments were conducted in the month of February.

EXAMPLE 2

In this case a nursery with large plantations of fruit trees was usedfor the field experiment. The plantations had frequent visits of bothroyal stag and roe deer causing substantial browsing damages.

The experiments were conducted in the period February to April. Most ofthe time the ground was covered by snow so that it was easy to recordvisits of stag and roe deer in the plantations and their surroundings.

Repellent units of the same type as described in Example 1 wereprepared, this time impregnated with 10 mg androsterone and 10 mgdehydroepiandrosterone in combination. The repellent units weresuspended at intervals of 10 m around the field. The sleeves werecovered by plastic film to protect them against precipitation.

During the first 7 days there were no records of roe deer or stag in theprotected area. The 7th night one roe deer entered the area. The tracksshowed that the animal had been restless, and that it had soondisappeared without browsing on the fruit trees.

After this observation there was no recorded visit from roe deer or stagduring 38 days.

On the 45th day counted from the beginning of the experiments trackswere recorded of a stag which had acted similarly to the roe deerpreviously referred to. Neither this animal had browsed on the fruittrees.

The tracks of a herd of 12 to 15 stags and several roe deer regularlyappeared in the vicinity of the experimental area during theexperimental period, but traces of these animals were not found closerthan approximately 100 m from the protected area, except for the twocases referred to above.

After 45 days the repellent units were removed. Already the first nightthe plantations were visited by both roe deer and royal stag whichcaused substantial browsing damages.

EXAMPLE 3

This experiment was conducted in a geographically isolated area having anumerous stock of roe deer. In this area there was an orchard which wasthe object of browsing damages from roe deer. Because of thegeographical isolation and the density of roe deer there was reason tobelieve that the normal caution of the animals and the fear of humanbeings may have been reduced.

Repellent units of the same type as described in Example 2 weresuspended in the outskirts of the orchard at intervals of about 10 m.

The ground within and immediately around the orchard consisted of loosesoil which made it easy to record the movements of the animals in thearea.

Before the start of the experimental period visits and browsing damagesby 3 to 5 animals each night were recorded. After the repellent unitswere positioned no visit of roe deer was recorded for an experimentalperiod of 45 days.

On two occasions during the experimental period tracks of roe deer wererecorded in the vicinity of the orchard. In those instances the animalshad approached the protected area in following wind and in high speed,and halted about 25 m from the repellent units and returned in longleaps.

When the repellent units were removed at the end of the experimentalperiod the roe deer returned already the first night in the same amountas previously with resulting substantial browsing damages.

EXAMPLE 4

This experimental series was conducted in a forest area having a densepopulation of elk and roe deer. An approximately 600 m long section ofgravelled forest road was chosen as an experimental area. By regularinspection it was possible to register how many animals followed orcrossed the road, since it was possible to read the tracks even in dryperiods.

In a control period of 6 days before the first repellent experimentthere were on the average 5 passages of elk and 2 passages of roe deereach day.

Extraction sleeves impregnated with 10 mg androsterone for each sleevewere suspended on both sides of the road at intervals of about 20 m.During an experimental period of 10 days no elks or roe deer passed theprotected section of the road. By inspecting other sections of theforest road it was possible to establish that there were still animalsin the area.

During a control period of 4 days after the repellent units had beenremoved there were on the average 4 passages of elk and 1 passage of roedeer each day.

Corresponding experiments were carried out on the same road section withrepellent units impregnated with 10 mg dehydroepiandrosterone,i-androsterone, oestrone, androsterone and 11-ketoaetiocholanalon,respectively. In all experiments the repellent units were suspended for10 days, whereas the control period was 4 days as in the firstexperiment. During the control periods between 3 and 7 passages of elkand between 1 and 3 passages of roe deer each day were observed. Duringthe experimental periods an average of 1 passage of elk each day wasnever exceeded. In no instance the animals had followed the entire roadsection, which was frequently the case during the control periods.

EXAMPLE 5

This experiment was conducted in an area having a dense elk population,and as in Example 4 a gravelled forest road was used. The length of theexperimental period was 10 days as in Example 4, the control periodbeing 4 days.

Repellent units prepared from extraction sleeves as in Examples 1 to 4were used. The sleeves were impregnated with the following steroidcombinations:

(a) 10 mg androsterone and 10 mg dehydroepiandrosterone.

(b) 1 mg androsterone and 20 mg testosterone.

(c) 100 mg dehydro-epi-androsterone and 5 mg 11-ketoaetiocholanalone.

(d) 0.1 mg androsterone and 60 mg androstanalone.

(e) 25 mg androsterone and 25 mg androstenol.

(f) 30 mg testosterone, 10 mg dehydroepiandrosterone and 0.05 mgoestrone.

In the experimental periods with the combinations a and c there were nopassages of elk, whereas up to one passage of elk each day was observedwith the remaining steroid combinations.

In the control periods between the experiments between 4 and 7 passagesof elk each day occurred.

EXAMPLE 6

In these experiments the repellent units were manufactured from conicalaluminum sleeves having an inner coating of cellulose. The cellulosecoating was impregnated with acetone solutions of various steroidmixtures as indicated below.

An orchard situated in a district having a very dense population of roedeer and being pested by roe deer browsing on the fruit trees, was usedan experimental area.

Before the experimental series was started an average number of 6 roedeer each night visiting and browsing in the orchard was recorded byobservation of track prints in the soft ground. The repellent units weresuspended at intervals of 7 m around the orchard and approximately 1.5 mabove the ground. Observations of track prints were made each morning.Each evening the ground surface was raked to facilitate observation ofany track prints.

    ______________________________________                                                                           Total                                                        mg               number of                                  Experi-                                                                             Steroid     in each Experimental                                                                           roe deer in the                            ment  mixture     unit    period, days                                                                           period                                     ______________________________________                                        g     cortisone   10      8        1                                                progesterone                                                                              10                                                          h     none                4        18                                         i     corticosterone                                                                            5                                                                 androsterone                                                                              5       8        0                                                11.sup.d -desoxy-                                                             cortisol    5                                                           j     none                4        21                                         k     corticosterone                                                                            5       8        0                                                11.sup.d -desoxy-                                                             cortisol    5                                                                 cortisone   5                                                                 progesterone                 2                                          l     none                4        16                                         m     androstenol 1                                                                 cortisone   10      8        3                                                corticosterone                                                                            10                                                          n     none                4        19                                         o     prednisolone                                                                              10                                                                oestriol    3       8        1                                                21-desoxy-                                                                    cortisone   5                                                           ______________________________________                                    

EXAMPLE 7

This experiment was conducted in order to study the long term effect ofthe repellent substance. An orchard situated on an island surrounded byopen water the year round was chosen as an experimental area. A largepopulation of roe deer and a smaller population of hart were present onthe island. The total damage on fruit trees and other useful plants bythe animals was very extensive. Because of the isolated situation of theisland it may be presumed that no or at most sporadic communication withother populations of deer and hart occurs.

The repellent units were shaped in the same manner as described inExample 6, i.e. they consisted of conical aluminium sleeves having aninner coating of cellulose. The cellulose coating was impregnated withan acetone solution of steroids in such an amount that each repellentunit contained 10 mg dehydro-epi-androsterone and 10 mg androsterone.

The repellent units were suspended around the orchard at intervals ofabout 8 m and approximately 1.5 m above the ground. Except for shortercontrol periods the experiment lasted for 18 months, which involved thata new generation of animals experienced the repellent substance, andthat it should be possible to observe any familiarization effects.

The experimental area was inspected every day for trace of deer andhart. Depending on the time of the year it was possible to observetraces either as track prints in snow or loose soil or as fresh browsingdamages on trees. Four control periods of one week each were included inthe experimental period. During the control periods all the repellentunits were removed. During all the four control periods numerous visitsof deer and hart could be observed already the first night.

During the experimental periods, in which the repellent units weresuspended, no visits of deer and hart were observed with the followingexceptions:

Days 48 to 50: Visits of 2 to 3 animals each night. During this periodthere was heavy wind with a wind force of between 15 and 25 m/s, andsome of the repellent units were destroyed. After the weather hadimproved and the damaged units replaced the protection was againeffective.

Day 63: One animal entered, but the track prints showed that the animalhad quickly turned around and returned the way it entered.

Days 92 to 96: Traces of one animal were found each morning. A closerinspection disclosed that the animal concerned was a lonely one year oldroe fawn which seemed to be hurt. The animal was killed and anexamination of the body showed that one of the legs was heavily damagedby shot.

Days 207 to 212: Visits by several animals each night. During thisperiod there was heavy wind and snow fall, and the number of animals wasconsequently difficult to ascertain.

Days 369 to 370: Visits by one and two animals respectively. Externalreasons why the animals had entered could not be determined.

Day 486: One animal had entered and according to the track prints it hadrun back and forth, whereupon it had left the area in long leaps.

During the entire experimental period animals and traces of animalscould be observed in the vicinity of the experimental area. Traces couldbe observed as close as 25 m from the suspended repellent units.

The term steroids may seem comprehensive, but this is not true regardbeing had to the fact that steroids form a very well defined group ofchemical compounds having a common basic structure and varying onlyslightly as far as substituents and double bonds are concerned. Thesteroids used in the experiments have been carefully selected in orderto form a representive selection of the group of substances defined inthe claims.

As appearent from the claims the invention is restricted to the use ofindividual or a small number of steroids at a time. The steroids usedare synthetic or extracted from naturally occurring materials by anysuitable chemical or physical isolation process.

We claim:
 1. A method for repelling animals by placing smellingrepellent substances in the area from which the animals are to be keptoff, characterized by the use as a repellent substances of one or moresteroids which are synthetic or have been extracted from naturallyoccurring materials and which are of the type occurring on human skin orhair or in human sweat or urine and/or of one or more of the derivativesthereof obtainable by subjecting the steroids to air, moisture ormicro-organisms in such a manner as to provide in the air aconcentration perceptible to the sense of smell of the animals, saidsteroids being selected from the group consisting of testosterone,androsterone, dehydroepiandrosterone, 11-ketoaetiocholanalone,i-androstanalone, oestrone and androstenol.
 2. The process of claim 1further characterized by the use as a repellent substance ofandrosterone or dehydroepiandrosteone or mixtures comprisingandrosterone and dehydroepiandrosterone.
 3. Means for repelling animals,characterized in that as a repellent substance it contains one or moresteroids which are synthetic or have been extracted from naturallyoccurring materials, and which are of the type occurring on human skinor hair or in human sweat or urine, and/or of one or more of thederivatives thereof obtainable by subjecting the steroids to air,moisture or micro-organisms, and that this repellent substance iscombined with a carrier into a repellent unit capable of liberatingmolecules of the repellent substance into the air for maintaining aconcentration perceptible to the sense of smell of the animals, furthercharacterized in that said steriods are selected from the groupconsisting of testosterone, androsterone, dehydroepiandrosterone,11-ketoaetiocholanalone, i-androstanalone, oestrone and androstenol. 4.The process of claim 3 further characterized in that the steroid isandrosterone or dehydroepiandrosterone or mixtures comprisingandrosterone and dehydroepiandrosterone.
 5. The process of claim 1further characterized in that the repellent substance is a mixture oftwo or more steroids or steroid derivatives and the steroids areselected from the group consisting of testosterone, androsterone,dehydroepiandrosterone, 11-ketoaetiocholanalone, i-androstanalone,oestrone and androstenol.
 6. Method according to claim 1 characterizedby placing one or more repellent units on or at the borders of the areafrom which it is desired to repel the animals.
 7. The process of claim 1characterized by placing one or more repellent units on or at theborders of the area from which it is desired to repel the animals andfurther characterized in that the amount of repellent substance for eachrepellent unit is between 1 ng and 100 mg.
 8. Means according to claim 3characterized by the amount of repellent substance in each repellentunit being between 1 ng and 100 mg.
 9. Means according to claim 8characterized in that the repellent substance is androsterone ordehydroepiandrosterone or mixtures consisting of androsterone anddehydroepiandrosterone.